1. Field of the Invention
The present invention relates to a method for generating a protective cover for a device, and particularly for generating a protective cover for devices containing areas whose function would be affected by injection molded packages, such as BAW filters (BAW=bulk acoustic wave), resonators, sensors and/or actuators. Particularly, the present invention relates to a method for generating such a protective cover for the devices on wafer level.
2. Description of the Related Art
Conventionally, devices are generated on and/or in a substrate, wherein after completing the device, the substrate comprising the device is disposed in a protected way in an injection molded package. In this arrangement, the substrate and the device are fully embedded into the material of the injection molded package, at least in the area of the device. This procedure is disadvantageous for devices whose function is affected by this material, which thus require a clearance for a proper functionality, such as it is, for example, required in the above-mentioned BAW filters, resonators, sensors and actuators.
One solution known in the prior art to solve this problem with injection molded packages is to provide a “counter substrate”, into which a respective opening is inserted, so that during the assembly of the device substrate and the package substrate, the cavity is disposed in the area of the device in the device substrate, so that no longer any effect on the functionality of the device occurs. On the wafer level, respectively, a wafer is generated with the respective patterns for the devices (system wafer), which is connected, for example by a bond procedure, to a second wafer (lid wafer), which has respective trenches and holes, which are for example made by etching the same. In that way, the trenches of the second wafer will form cavities across the sensitive pattern of the first wafer, whereby the contact pads of the first wafer are accessible through the holes in the second wafer. Thereby, the sensitive patterns are protected.
As an alternative to the above-described procedures, a ceramic package can be used.
The disadvantage of the above-described known solutions for ensuring the functionality of the devices is that there is always a second substrate and a second wafer to be patterned, which requires processing and handling separate from the first wafer. This leads to a very expensive total production and further increases the requirements with regard to the required process accuracy.